Expanded fastener for a honeycomb structure and method of assembly

ABSTRACT

An expanding panel fastener assembly for affixing a honeycomb panel structure to a support structure is disclosing having an insert member that attaches to a hole drilled within the honeycomb panel. A flexible sleeve and retainer assembly includes a molded flexible sleeve, an expander member and a retainer member. A sleeve spacer can further be attached to the flexible sleeve to assist in retaining it within the insert member. By providing a fastener for engagement with the retainer member, the expander member can further prevent withdrawal of the retainer member and can further assist in expanding the flexible sleeve to provide a sealing configuration with any support structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Provisional Application Ser. No.60/439,512 filed on Jan. 13, 2003, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a panel fastener assembly includingan elastomeric sleeve and retainer assembly that can be inserted througha hole in a panel for receiving fasteners to secure the fastener to thepanel and a support substrate.

2. Description of Related Art

In the field of aircraft and aerospace craft assembly, lightweightpanels such as honeycomb panel structures are utilized and are mountedto bulkheads and aluminum intercostal ribs or beams that extend withinthe exterior housing of the aircraft structure.

Various prior art methods of attaching honeycomb panels as floors orwalls in aircraft manufacturing frequently requires the use of a femalethreaded clip nut which is separately attached to the aircraftstructure. The clip nut can be formed of sheet metal steel to hold, forexample, a hexagonical nut, and after the ribs or beams have beenappropriately drilled for mounting holes, the clip nut can then belocated so that a fastener will be inserted through a insert such asfound, for example, in U.S. Pat. No. 6,298,633 for securing a honeycombpanel to the support structure. A large number of such clip nuts andfasteners are utilized to provide sufficient locking force and fastenerssuch as a screw is then inserted through the hole and threaded throughthe clip nut to hold the panel. Problems, however, have occurred in theadditional labor that is required in the insertion and alignment of theclip nuts with the corresponding holes in the support structure. As apractical matter, when a honeycomb panel is installed, some attachmentpoints frequently are found not to have the clip nuts properly installedand, for example, if the honeycomb structure is a floor board, it mayhave to be removed, new clip nuts installed, and then the floor boardreinstated. The same problem can occur if the clip nut becomes strippedupon the insertion of the fastener.

Another problem that can occur with the clip nut installation onaircraft structure is possible galvanic corrosion that can be caused bythe clip nut scratching and interacting between the aircraft structureand inserts in the floor boards and walls. Since there is aniron-aluminum interface, corrosion can occur.

Additionally, the clip nuts can cause the floor boards in the wall to beslightly raised off the appropriate attachment structure such as theintercostal ribs or beams. This problem further causes the walls andfloor to resonate and can create unnecessary noise and vibration. Suchvibration can again create scratching to permit a direct metal-to-metalcontact to thereby provide corrosion.

Additionally, misalignment problems are more prone to occur with use ofthe individual clip nuts.

Accordingly, the prior art is still seeking to resolve these problems sothat the panel structure can be securely held in an accurate andefficient manner while eliminating corrosion problems and high laborcosts.

SUMMARY OF THE INVENTION

An expanding panel fastener assembly for affixing a honeycomb panelstructure to a support structure includes an insert member of aconfiguration for attaching through a hole that is bored or drilledthrough a honeycomb panel. Insert members of numerous differentconfigurations can be utilized and as such, forms only one possiblecomponent in one form of the present invention. A flexible sleeve andretainer assembly has a configuration to extend through the installedinsert member and the corresponding support structure whereby a portionof the assembly will be retained by the insert member. The flexiblesleeve and retainer assembly includes a moldable flexible sleeve, anexpander member and a retainer member. A fastener member of aconfiguration that extends through the flexible sleeve when installed inthe panel and further through the support structure and therebyoperatively engages the retainer member such as a nut member is utilizedto complete the assembly. Tightening of the fastener member such as ascrew relative to the nut member will expand the expander member belowthe support structure to thereby prevent withdrawal of the nut member.Additionally, this flexible sleeve is also compressed and expanded sothat it can further provide a sealing configuration with the supportstructure. Since the flexible sleeve is relatively movable, misaligmnentproblems can be addressed within certain tolerances, and issues ofvibration and corrosion can be significantly reduced.

An operation and method of fastening an aircraft panel structure to asupport structure in an aircraft can comprise the steps of providingopenings in the panel structure such as a honeycomb structure byappropriately drilling or reaming holes at predetermined locations.Insert members can then be inserted through the panel openings usuallywith a flange on one side and a bending of a lip configuration on theother side to thereby establish a structurally strong opening in, forexample, a honeycomb panel. A large number of such openings in ahoneycomb panel can be utilized to provide a sufficient attachment forceto the support structure such as intercostal ribs or beams in anaircraft. A flexible sleeve and retainer assembly may be insertedthrough each of the insert members in the panel structure. The panel isthen aligned with a support structure having complementary openings forreceiving the flexible sleeve and retainer assemblies.

Finally, fastener members such as screws can be inserted through thepanel within the flexible sleeve that also extends through the supportstructure opening. The fastener member can then engage the retainermember such as a nut, and as the nut is tightened, the fastener memberwill expand an expander member, thereby preventing the nut member frombeing pulled through the opening in the support structure.

The operative engagement of the fastener member with the retainer membersuch as a nut can further compress the flexible sleeve which can beformed from rubber or a silicone material to thereby further sealagainst the support structure and help reduce any vibration andcorrosion issues.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention, which are believed tobe novel, are set forth with particularity in the appended claims. Thepresent invention, both as to its organization and manner of operation,together with further objects and advantages, may best be understood byreference to the following description, taken in connection with theaccompanying drawings.

FIG. 1 is an exploded view of a panel, fastener assemblies andintercostal support ribs of an aircraft floor.

FIG. 2 is a cross-sectional disclosure of the insertion of an insertmember in a honeycomb panel.

FIG. 3 is a partial cross-sectional perspective view of the relationshipbetween the honeycomb panel, insert member and the flexible sleeve andretainer assembly.

FIG. 4 is a cross-sectional view of a fastener member entering a paneland support structure through the flexible sleeve.

FIG. 5 is a cross-sectional view showing the fastener member engaged andtorqued to the appropriate pressure.

FIG. 6 is an exploded view of the panel fastening system panel andsupport structure.

FIG. 7 is a top view of one portion of the expanding member.

FIG. 8 is a top plan view of another portion of the expanding memberintegral with a nut member.

FIG. 9 is a top plan view of an alternative expanding member; and

FIG. 10 is a perspective view of the expanding member of FIG. 9.

DETAILED DESCRIPTION OF TEE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention which set forth the best modes contemplated to carry out theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone of ordinary skill in the art that the present invention may bepracticed without these specific details. In other instances, well knownmethods, procedures, and components have not been described in detail asnot to unnecessarily obscure aspects of the present invention.

Features of the present invention overcome the following design issues:

-   -   1. The new fastener/insert needs to develop the same load        carrying characteristics as the existing insert clip-nut        combination.    -   2. The new fastener/insert needs to work as a replacement part        as well as a new aircraft assembly.    -   3. The new fastener/insert needs to have a positive secondary        locking device (fail safe).    -   4. The new fastener/insert must work within the original        installation hole and length requirement.    -   5. The new locking device needs to reduce or eliminate galvanic        corrosion.

The installation of this fastener assembly gives the user manyadvantages over prior art systems currently in use. The advantages ofusing this system are, but not limited to:

-   -   Labor reduction at assembly and maintenance cycles.    -   Elimination of an expensive component (clip nuts).    -   A fastener that is rebuildable from the topside surface of        panel.    -   A fastener that may reduce or eliminate galvanic corrosion.    -   A fastener that reduces noise levels in aircraft interior.

Floors and walls having this fastener can easily be removed andreinstalled. If the fastener sub-component should become unusable, thesub-assembly can be removed and replaced without removal of floors orwalls.

The clip nuts currently in use are the primary cause for initiation andpropagation of corrosion. The initial installation of the clip nutscratches the anodized and primed surface of the aircraft structure andexposes bare aluminum to the elements and thus starts corrosion. Use ofthis new fastener assembly eliminates that source of corrosion plus theelastomeric material in the assembly helps to isolate the fastener fromthe aircraft structure and provides a secondary advantage which is noiseisolation.

A housing insert 6 is permanently bonded to a honeycomb sandwich panel2. The housing insert 6 can support a working assembly and relatedcomponents. The flexible sleeve and retainer assembly 12 is molded fromelastomeric compounds, such as rubber or silicone material, for example,to meet a Boeing Specification BMS-83 for rubber. The assembly containsan upper insert portion 32 that creates thread-locking to meet therequirements of NASM-25027—Nut Self-Locking specification. The upperinsert 32 is molded permanently in the elastomeric compound. The nextsub-assembly components are a threaded nut segment 36 and a lowerfollower segment 38. These final two (2) components are also moldedpermanently into the elastomeric compound.

The insert housing 6 can have a flange 20 of 0.875 inches in diameterhaving a thickness of 0.02 inches. The body length is varied anddependent on panel thickness. Another external feature can be a radialgroove having two tapers on each side that is located mid body and has areduced diameter of about 30 percent of the body diameter that is usedto reduce weight. An optional feature on the exterior of the part is aknurled portion or irregular surface 24 next to the flange 20 that isused to retain the insert 6 after installation, for the purpose ofallowing the adhesive to cure. The upper internal feature is a taperedand reduced cross sectional rim 22 with a controlled counter bore depthdesigned to adjust for panel and skin thickness variations; this areawill become the flared area after installation. The other internalfeature is a controlled countersink diameter that controls screw heightafter installation.

The internal bore is modified to accept the upper portion of theelastomeric or flexible sleeve and retainer assembly 12 and the throughhole will be modified to allow the retainer assembly 12 (describedbelow) to have radial float as to compensate for any panel holemisalignment.

The preferred material for the housing for the purpose of thisdescription will be aluminum but is not limited to that material.

The upper insert portion 32 of the retainer assembly 12 will bemanufactured preferably from stainless steel but is not limited to thismaterial selection. The upper insert portion 32 can be tapered on theoutside diameter to match the internal taper on the housing. The outsidediameter will also have a radial groove to reduce weight and increasethe surface area to allow better elastomer bonding. This upper insertportion engages the major diameter of the installation screw thread toprovide locking torque per NASM-25027 requirements. The end of theinsert portion facing upward will have a countersink to match the flathead configuration of the installation screw, flat head design, but isnot limited to that single shape screw. The lower end of the insertportion will have a counter bore that will be used to connect andincrease the tensional resistance of the elastomeric portion to beattached later in the assembly process containing the two lowersegments.

Two lower components make up a lower assembly (1 nut segment and 1follower segment). A distinguishing feature that further separates thisnut and follower from a standard nut and follower design is that thecenterlines of each component are 0.03 inches offset in oppositedirections to each other as assembled so that when a fastener 14 isinserted, the components will expand to lock against any removal force.

The material is stainless steel but is not limited to that material. Thedimensions of the nut segment are the same as the follower 0.100 thickand 0.03 inches offset, the thread is 10-32 UNJ-3B for a standardinstallation screw for this size; there is no truncation. An additionalfeature of the nut segment is an arm of material protruding in theopposite direction of the offset with a height that matches the followersegment thickness and fills in the truncated part of the followersegment. This extra piece of material allows the nut and expandingfollower to contact the bottom surface of the structure and keeps theassembly from tilting, thus allowing the installed fastener assembly toresist pull out.

The follower segment material is also stainless steel but not limited tothat material. The dimensions are 0.100 thick with a 0.030 offsetthrough hole. The segment is truncated in the direction of the offset;this allows one side of the segment to be displaced radially outwardwhen the installation screw is engaged.

The following is one method to assemble the sub-assembly components ofthis invention.

After completing the machining and plating processes, the three (3)components are assembled into a die for elastomeric molding. The moldcreates a tapered portion of elastomeric material around the uppersegment. As part of the upper segment component, the mold creates asection of elastomeric material plug on the lower part of the segmentthat fills the counter bore. This portion of elastomeric material doestwo (2) things: first it starts the long section that will contain thetwo (2) follower elements and creates a larger bonding surface. Secondas a stiffener it also increases the torsional stiffness of the lowersub-assembly during final assembly. In this and any other embodiment ofthis invention, one can include an armature of fibers or reinforcingmesh to aid the stiffness and durability of the elastomeric material.This completes the assembly of the sub-assembly.

Preparation of the honeycomb panel 2 consists of drilling aninstallation hole 8. Most installation holes 8 are controlled in thisprocess. For the purpose of this disclosure the installation hole is0.455 inches in diameter. The installation hole diameter is a functionof a selected size of fastener and panel and is not to be limited to0.455 inches diameter. The housing portion of the assembly is bonded tothe bottom outside skin of the honeycomb sandwich panel 2 with the useof adhesive. The type of adhesive used for bonding is controlled by theend user of the fastener, but for the purpose of this disclosure it canbe Epi-Bond 420 but not limited to that selection.

Adhesive is applied to the top side of the flange 20 of the housinginsert 6 or to the honeycomb panel surface 18 around the installationhole. Install the panel fastener housing insert 6 into the installationhole 8 up to the panel retention feature (knurl) 24. Press down on theback of the insert flange until the flange pops in and bottoms outagainst the panel skin. Using an installation-flaring tool 26, put thepilot into the through hole until the tool stops against the top of thehousing insert 6. Using a press or a device that will create acompression load, press down until the installation tool stops againstthe top of the panel. The housing insert 6 is now fully installed.Curing of the adhesive should be carried out according to adhesivemanufacturer's instructions.

The final part of the assembly is to put the assembled honeycombsandwich panel into the aircraft. After the preliminary location of thepanel is found, put the flexible sleeve and retainer assembly 12 intothe housing inserts 6. Acquire the appropriate assembly screw 14 andinstall through the upper insert portion until resistance is feltthrough the screw. Start turning the screw clockwise until the finalassembly torque is reached. During the torquing sequence the lowerassembly elements are drawn up against the support structure. As thelower assembly is drawn up by the screw action, the external surfaces ofthe elastomeric material 34 expand radially outward, creating a positiveseal between the panel fastener and the aircraft structure. Thispositive seal provides pull out strength (fail safe), and noise andvibration dampening.

Removal of the honeycomb sandwich panel 2 is accomplished by removingthe installation screws and separating the panel from the structure. Theelastomeric sub-assembly of the panel fastener may be left inside thehousing or easily removed and replaced with a new sub-assembly.

As can be seen in FIG. 1, the intercostal ribs or beams 4 can, forexample, be a U- or C-shaped aluminum beam 4 with appropriate holes 10that are predrilled at desired locations. Corresponding holes 8 areprovided within the panel insert 2 which, for example, as shown, can bea honeycomb structure as known in this field. A large number ofdifferent housing inserts 6 can be preinstalled in the panel insert 2.The procedure for such installation is shown, for example, in FIG. 2where a flange 20 of the insert housing 6 can be adhesively applied to alower panel surface 18. When placed on a support surface, a compressiontool 26 can then be applied to spread the upper rim 22 locking theinsert housing 6 within the panel housing. The upper panel surface 16can be compressed downward to insure an upper flat surface. At the baseof the body of the insert housing 6 adjacent the flange 20, a knurledsection can help align and fasten the insert housing 6 during theinstallation procedure. This can be seen in FIG. 3 of our presentdrawings. Additionally, the flange 20 can optionally have weightreducing holes 30 if desired.

With the completion of the attachment of the insert housing 10 to thepanel 2, the panel assembly is now ready to receive the flexible sleeveand retainer assembly 12 which can have a conical upper surface forinterfacing with the interior diameter of the housing insert 6. As canbe appreciated, various configurations and designs are possible withinthe parameters of the present invention since the prime purposes is topreassemble retainer assemblies 12 prior to aligning the panel assembly2 with the aircraft support structure 4 as shown in FIG. 4. As can beseen, the flexible sleeve and retainer assembly 12 is of a length toadequately extend through the hollow insert housing 6 and the hole 10within the U-beam 4. The molded rubber sleeve 34 captures a sleevespacer 32, and in the embodiment of FIG. 4, a lower retainer member suchas a nut 36 having an integral expander portion 40. Also molded withinthe tubing rubber sleeve 34 is a complementary expander member 38 thatis not directly affixed to the retainer nut 36.

As shown in FIG. 5, when the fastener such as an elongated screw 14extends through the expander member 38, it displaces this componentradially outward to thereby prevent retraction of the nut 36 backthrough the hole 10 in the beam 4.

It should be appreciated that other configurations of expanding memberscan be utilized such as the split ring expander 42 shown in FIG. 9 andFIG. 10. In this alternative arrangement, the nut or retainer member 36can be of a conventional configuration and is separate from the splitring expander 42. The split ring expander 42 has a thickness indimension that again will prevent removal of the nut through the opening10 in the support beam 4. To accommodate this expansion, an axialpivoting rib groove 44 can be positioned across from an opening in thesplit ring expander 42. As shown in FIGS. 9 and 10, split ring expander42 is also embedded within the rubber sheath or tubular sleeve 34.

Referring again to FIG. 5, as the expander member 38 prevents withdrawalof the nut 36 from the undersurface of the support beam 4, the rubbersleeve 34 can be crimped to provide a seal against the undersurface ofthe beam 4. This helps prevent any corrosion effect and also can act asa vibration damper.

Referring to FIGS. 6 through 8, an exploded view of the assemblyincluding the first embodiment of the expander member 38 is shown. Ascan be seen, the center of the expander member 38 is offset from thecenter of the nut 36 so that it is displaced radially outward when thefastener 14 is inserted. As can be appreciated, however, this is aschematic view in FIG. 6 since the rubber sleeve 34 is molded about thesleeve spacer 32, retainer nut 36 and the expander member 38.

In summary, the present invention describes both an axially displacedexpanded internally threaded panel fastener for a honeycomb structureand a method of assembly. As can be readily appreciated, this structureutilizes an elastomeric sleeve and nut assembly that provides a numberof improvements against vibration, corrosion and misalignment, and sucha structure could be used independently with a panel or, as shown in thepreferred embodiment, for attaching to a substructure in the aircraft.

Although the present invention has been fully described in connectionwith the preferred embodiment thereof, it is to be noted that variouschanges and modifications apparent to those skilled in the art are to beunderstood as included within the scope of the present invention asdefined by the appended claims unless they depart therefrom.

Those skilled in the art will appreciate that various adaptations andmodifications of the just-described preferred embodiment can beconfigured without departing from the scope and spirit of the invention.Therefore, it is to be understood that, within the scope of the amendedclaims, the invention may be practiced other than as specificallydescribed herein.

1. An elastomeric sleeve and retainer assembly for insertion through ahole in a panel for receiving a fastener to secure the fastener to thepanel, comprising; a retainer member; an elastomeric sleeve attached tothe retainer member; and an expander member attached to the elastomericsleeve whereby when a fastener engages the retainer member to draw ittoward an interior surface of the panel the expander member expands toprevent withdrawal of the retainer member through the hole.
 2. Theelastomeric sleeve and retainer assembly of claim 1 wherein theelastomeric sleeve is a flexible sleeve that can collapse duringassembly to seal the retainer assembly to the panel.
 3. The elastomericsleeve and retainer assembly of claim 1 wherein the elastomeric sleeveis a moldable rubber.
 4. The elastomeric sleeve and retainer assembly ofclaim 1 further including a sleeve spacer attached to the elastomericsleeve for securing the elastomeric sleeve in the hole.
 5. Theelastomeric sleeve and retainer assembly of claim 1 wherein the expandermember is of a split-ring configuration with a first part formedintegral with a nut member and a second part held adjacent to the firstpart by the elastomeric sleeve.
 6. The elastomeric sleeve and retainerassembly of claim 1 wherein the expander member is of split-ringconfiguration with an opening on one side and a pivotable portion on anopposite side.
 7. The elastomeric sleeve and retainer assembly of claim1 wherein the elastomeric sleeve is a hollow tube with an exteriorconical opening and having an internal surface of a configuration tosupport the retainer member and expander member.
 8. An expanding panelfastener assembly for affixing a honeycomb panel structure to a supportstructure comprising: an insert member of a configuration to attach to ahoneycomb panel through a hole in the honeycomb panel; a flexible sleeveand retainer assembly of a configuration to extend through the insertmember and support structure and to have a portion retained by theinsert member including a flexible sleeve, an expander member and a nutmember; and a fastener member of a configuration to extend through theflexible sleeve and support structure and to operatively engage the nutmember, whereby tightening of the fastener member relative to the nutmember expands the expander member to prevent withdrawal of the nutmember and expands the flexible sleeve to provide a sealingconfiguration with the support structure.
 9. The expanding panelfastener assembly of claim 8 wherein the flexible sleeve is an elongatedtube with the expander member and nut member at one end of the elongatedtube and the insert member contacting the other end of the elongatedtube, an intermediate portion of the elongated tube is flexible toaccommodate alignment with a support structure.
 10. The expander panelfastener assembly of claim 9 further including a sleeve spacer mountedwithin the elongated table.
 11. The expanding panel fastener assembly ofclaim 10 wherein the expander member is of a split-ring configurationwith a first part formed integral with a nut member and a second partheld adjacent to the first part by the elastomeric sleeve.
 12. Theexpanding panel fastener assembly of claim 10 wherein the expandermember is of split-ring configuration with an opening on one side and apivotable portion on an opposite side.
 13. The expanding panel fastenerassembly of claim 10 wherein the elongated tube is a moldable rubberwith an exterior conical opening at the one end surrounding the sleevespacer and an internal surface of a configuration to integrally supportthe expander member and retainer member at the other end.
 14. A methodof fastening an aircraft panel structure to a support structure in anaircraft comprising the steps of: providing an opening in a panelstructure; fastening an insert member in the panel opening; fixedlyinserting a flexible sleeve and retainer assembly through the insertmember, the flexible sleeve and retainer assembly including a flexiblesleeve, an expander member and a retainer member; aligning the panel andflexible sleeve and retainer assembly with a support structure having acomplimentary opening for receiving the flexible sleeve and retainerassembly; and inserting a fastener member through the flexible sleeveand the support structure opening to operatively engage the retainermember and to expand the expander member whereby the panel structure isattached to the support structure.
 15. The method of claim 14 whereinthe operative engagement of the fastener member with the retainer memberfurther compresses the flexible sleeve to seal against the supportstructure.